The invention relates to a method for the manufacture of a roller which on its cylindrical outer surface is provided with a pattern of indentations (a so called screen roller). Normally a screen roller consists of a thick-walled or full metal cylinder in the surface of which a screen pattern has been applied by means of an appropriate technology for instance by applying a brayer after which this screen pattern is provided with a hard wear layer. These rollers must satisfy to very high precision requirements concerning geometry and finish, as well as centering and are therefore expensive. As a consequence of its use, wear in course of time will occur at the surface and damages will also appear, after which an expensive overhaul must be performed by the manufacture or in a specialized enterprise. The transport of the heavy and vulnerable rollers is expensive whilst the rollers to be reconditioned are not available for a long period. The keeping in stock of reserve rollers necessitates a great investment.
The invention aims at providing a method for the manufacture of a screen roller which does not possess these disadvantages. According to the invention this is obtained by starting from a hollow thick-walled or massive roller (a socalled support cylinder) around which a thin-walled cylindrical sieve is pushed, after which this sieve is clampingly mounted upon the support cylinder. By means of this method one obtains a screen roller composed of a smooth-walled support cylinder around which a thin sieve is secured. Such a screen roller can be applied for the even distribution of ink upon another roll, for instance in an off-set process.
A practical advantage of the invention can be obtained when the perforations of the sieve are first closed by applying a fluid impervious layer, whereby subsequently during the pushing up, a pressure fluid is supplied between the support cylinder and this sieve for the expansion of the sieve and the facilitating of the pushing up movement. Hereafter the supply of pressure fluid is ended. When the fluid impervious layer is applied against the inner side of the cylindrical sieve, then it is even possible to obtain an easily transformable screen roller. The pushing up as well as the removal of the sieve can in that case take place at any moment.
When the fluid impervious layer is applied to the outerside of the sieve, this layer must be removed after the mounting of the sieve in order to obtain the intended screen roller. The sieve can also be rendered temporarily impervious by filling up the holes (meshes). For the removal of the sieve it is then every time required that the sieve is once again rendered impervious. When the outer layer of the screen roller (which means the sieve) is worn out after the period of use of the screen roller, the old sieve can be cut open and consequently be removed from the support cylinder. Hereafter a new sieve adapted to the circumstances can be mounted upon this support cylinder without much lost of time.
A further aspect of the invention relates to an apparatus for performing the above described method, comprising a support cylinder embodied as a hollow thick-walled or a massive roller. According to the invention this apparatus is distinguished in that the support cylinder is provided on at least one of its front faces with at least one radial passage which opens at the outer periphery of this support cylinder, a connection being present for communication with a source of pressure fluid. This pressure fluid is mostly air, but may also be a liquid by means of which a thin-walled cylindrical sieve or screen stencil can be pushed upon the support cylinder or can be removed from it.
In an embodiment making use of a hollow thick-walled roller, this roller is at both ends provided with a support axle having a disc-shaped portion which is clampingly pushed in the concerning end of the roller, the radial passages consisting of a number of bores which at their innermost end empty into axial channels in the disc-shaped portion, a channel in the other disc-shaped portion being provided with the desired pressure fluid connection. Both disc-shaped portions render it possible that a cylindrical screen stencil having a removable impervious inner- or outer layer, can be pushed upon, or removed from the support cylinder by means of a layer of pressure fluid between said cylinder and the screen stencil.
It is however also possible to mount the sieve in a different manner clampingly around the smooth support cylinder. In that case one uses a sieve (screen stencil) within which latent crimping tensions are applied. After the pushing of the sieve upon the support cylinder--which sieve in this case should have a somewhat greater diameter than said cylinder--the sieve is being subjected to a thermal treatment in order to free the latent crimp tension in order to crimp the sieve upon the support cylinder .